Commit 275e6e1e authored by Paolo 'Blaisorblade' Giarrusso's avatar Paolo 'Blaisorblade' Giarrusso Committed by Linus Torvalds
Browse files

[PATCH] uml: fix compilation and execution with hardened GCC 



To make some half-assembly stubs compile, disable various "hardened" GCC
features:

*) we can't make it build PIC code as we need %ebx to do syscalls and GCC
   wants it free for PIC

*) we can't leave stack protection as the stub is moved (not relocated!) in
   memory so the RIP-relative access to the canary tries reading from an
   unmapped address and causes a segfault, since we move the stub of various
   megabytes (the exact amount will be decided at runtime) away from the
   link-time address.

Signed-off-by: default avatarPaolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Acked-by: default avatarJeff Dike <jdike@addtoit.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent cb8aa3d2

arch/um/Makefile

+5 −1
Original line number Diff line number Diff line
@@ -118,6 +118,10 @@ prepare: $(ARCH_DIR)/include/kern_constants.h 
LINK-$(CONFIG_LD_SCRIPT_STATIC) += -static

LINK-$(CONFIG_LD_SCRIPT_DYN) += -Wl,-rpath,/lib



CFLAGS_NO_HARDENING := $(call cc-option, -fno-PIC,) $(call cc-option, -fno-pic,) \

	$(call cc-option, -fno-stack-protector,) \

	$(call cc-option, -fno-stack-protector-all,)



CPP_MODE-$(CONFIG_MODE_TT) := -DMODE_TT

CONFIG_KERNEL_STACK_ORDER ?= 2

STACK_SIZE := $(shell echo $$[ 4096 * (1 << $(CONFIG_KERNEL_STACK_ORDER)) ] )
@@ -227,4 +231,4 @@ $(ARCH_DIR)/include/kern_constants.h: $(objtree)/$(ARCH_DIR)/include 
	@echo '  SYMLINK $@'

	$(Q)ln -sf ../../../include/asm-um/asm-offsets.h $@



export SUBARCH USER_CFLAGS OS
 
export SUBARCH USER_CFLAGS CFLAGS_NO_HARDENING OS

arch/um/kernel/skas/Makefile

+8 −1
Original line number Diff line number Diff line
@@ -11,4 +11,11 @@ USER_OBJS := clone.o 
include arch/um/scripts/Makefile.rules



# clone.o is in the stub, so it can't be built with profiling

$(obj)/clone.o : c_flags = -Wp,-MD,$(depfile) $(call unprofile,$(USER_CFLAGS))
 
# GCC hardened also auto-enables -fpic, but we need %ebx so it can't work ->

# disable it



CFLAGS_clone.o := $(CFLAGS_NO_HARDENING)



# since we're setting c_flags we _must_ add $(CFLAGS_$(*F).o).



$(obj)/clone.o : c_flags = -Wp,-MD,$(depfile) $(call unprofile,$(USER_CFLAGS)) $(CFLAGS_$(*F).o)

arch/um/sys-i386/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -13,6 +13,8 @@ USER_OBJS := bugs.o ptrace_user.o sigcontext.o fault.o stub_segv.o 
USER_OBJS += user-offsets.s

extra-y += user-offsets.s



CFLAGS_stub_segv.o := $(CFLAGS_NO_HARDENING)



extra-$(CONFIG_MODE_TT) += unmap.o



include arch/um/scripts/Makefile.rules

arch/um/sys-x86_64/Makefile

+2 −0
Original line number Diff line number Diff line
@@ -21,6 +21,8 @@ USER_OBJS := ptrace_user.o sigcontext.o stub_segv.o 
USER_OBJS += user-offsets.s

extra-y += user-offsets.s



CFLAGS_stub_segv.o := $(CFLAGS_NO_HARDENING)



extra-$(CONFIG_MODE_TT) += unmap.o



include arch/um/scripts/Makefile.rules

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